Neuromodulation has been variously defined as a) the science of how electrical, chemical, and mechanical interventions can modulate or change central and peripheral nervous system functioning; b) the form of therapy in which neurophysiological signals are initiated or influenced with the intention of altering the function and performance of the nervous system and achieving therapeutic effects, or c) the therapeutic alteration of activity in the central, peripheral or autonomic nervous systems, electrically or pharmacologically, by means of implanted devices. Implantable devices, however, carry a certain risk of surgical complications (e.g. infection, scarring), are limited by the current that can be used for therapeutic purposes, and dictate the need to avoid the electromagnetic and electrical fields that may interfere with function of the device.
Transcranial electrostimulation (TES) is a collective term for a variety of noninvasive electrotherapeutic techniques where electrical current is administered through electrodes positioned on the skin of the subject's head. TES has been reported to produce a plethora of non-pharmacological, natural therapeutic effects, including analgesia, anxiolysis and stress reduction, enhancement of mood and cognition, positive effects in patients with neurodegenerative diseases and impaired neurological function, alleviation of symptoms of drug, alcohol and nicotine withdrawal, stimulation of immune system, acceleration of regeneration and tissue repair, and other.
The use of electrical currents for the purpose of producing narcosis or analgesia was pioneered by the French physiologist Leduc nearly 100 years ago. Over the next 70 years, several attempts were made to produce and maintain a state of general anesthesia by administering different parameters of electrical currents, applied to the skin of the subject's head (i.e., transcranially and transcutaneously). However, due to the high intensity of current required to induce general anesthesia, these efforts were abandoned and superseded by attempts to produce analgesia, rather than general anesthesia, by application of electrical currents. TES is decidedly different from transcutaneous electrical nerve stimulation (TENS), which applies electrical stimulation in the vicinity of the peripheral nerve(s) supplying the affected area in an attempt to provide pain relief to that area through activation of the low-threshold mechanoreceptive Aβ-fibers, which “close the gate” to the painful stimuli entering the spinal cord, as opposed to a systemic analgesia obtainable using TES. TES should also not be confused with another from of TENS called PENS (percutaneous electric nerve stimulation, sometimes also called PNT, percutaneous neuromodulation therapy), where the skin is pierced by electrodes.
Different types of Transcranial Electrical Stimulation (TCES, herein (“TES”)) are suggested in the literature under a wide variety of names, including Limoge current, Lebedev current, Cranial Electrotherapy Stimulation (CES), Low Current Electrostimulation, Auricular Microstimulation, and others [Limoge, 1999].
There is still a need for improved TES methods to treat or prevent pain and other various medical conditions.